Fort Zeelandia is the most important building complex in Dutch Formosa (1624-1662). Since the Dutch East India Company (VOC) came Taiwan in 1624 to set up a trading post, until its withdraw in 1662, this fort ceaselessly played a critical role in military, trade and governance. Due to its importance, many scholars have conducted research on this fort and tried to reconstruct its original appreance; however, so far, no scholar has proposed a complete and persuasive result of reconstruction. A previous paper, “Fort Zeelandia in the 17th-century Dutch Formosa: Its Construction Process and Relationship to the Early Modern Ideas of European Fortification Design” (Huang, 2021), has explored the form, construction and related historical events of Fort Zeelandia in different stages of the Dutch rule period according to historical documents, historical paintings and early modern ideas of European/Dutch fortification design. This paper also points out that the mid-1640s was the most representative period of this fort. At that time, its three major parts of Fort Zeelandia had been built, including the “upper main fort” (as a square plan with four bastions), the “lower main fort” (as a four-pointed-star plan with four round towers) and the “outer fort” (which has two bastions and one round tower), and so had the Governor’s House inside the fort. Moreover, the church inside the fort was completed in 1645. Based on the above-mentioned reasons, this study chose the architectural appearance of Fort Zeelandia in the mid-1640s as the object of reconstruction. In addition to reviewing the previous research results of Kuriyama Syunichi, Guo-En Ceng and Hui-Cheng Lin, four important sources for the reconstruction work were also taken into consideration in this paper. The first is about the site data of the fort, including the building remains, contour map and cadastral map. Second, some of the historical documents related to the 17th-century Dutch VOC should be referred to; the most important two doucments are the “Nicolaes Couckebacker’s Inspection Report to the Governor-general in Batavia” in 1639 and Die wundersamen Reisen des Caspar Schmalkalden nach West- und Ostindien 1642–1652 written by the VOC soldier Caspar Schmalkalden. Third, the historical paintings related to the Fort Zeelandia in the mid-1640s should be analyzed, including seven paintings between 1635 and 1652. Fourth, the reconstruction of the architectural appearance of Fort Zeelandia, especially the reconstruction of its each bastion, should correspond with the idea and principle of Dutch fortress design at that time, i.e. the so-called “Old-Netherlands System”. By means of the clarification and analysis of the above four important sources for the reconstruction work, the three major parts of Fort Zeelandia in the mid-1640s, i.e. the upper main fort, the lower main fort and the outer fort, were reasonably reconstructed, including their location, heights, plans and other details. In accordance with the reconstruction result, a physical model in a scale of 1:400 was made. Furthermore, this paper also combined the reconstructed plan of Fort Zeelandia with the plan of Zeelandia City also in the mid-1640s which was reconstructed in a previous paper, “Reconstruction of the Ground Plan of Zeelandia City in Taiwan in the Mid-1640s” (Huang, 2019), so that a whole picture of Zeelandia City at that time can be presented. The reconstruction result of the architectural appearance of Fort Zeelandia, together with its plan combination with the that of the city, can be used as a reference for the archaeological excavation on the site of Fort Zeelandia and as a basis for the follow-up research in the future.